Simple solid-electrolyte gamma-ray and relativistic-charged particle dosimeter

ABSTRACT

A gamma-ray and relativistic charge particle detector and method for measuring the amount of radiation passed through the detector. The detector is a dosimeter comprising a plurality of equally spaced batteries disposed to form a series of columns and rows within a plane having vertical and horizontal rectangular coordinate axes. The batteries, radiation sensors, can be repeatedly charged and discharged with very little characteristic change in the discharge curve. The batteries have a solid electrolyte and a low voltage output. Radiation passing through the electrolyte causes partial ionization of the electrolyte, which reduces the battery terminal voltage in proportion to the amount and type of radiation passed therethrough. Before and after being exposed to radiation, the batteries are placed in a test stand and the individual battery voltages are simultaneously measured and recorded. A change in voltage across the battery terminals, after exposure to a known type of radiation, is proportional to the radiation passed therethrough. Thus, differential voltage, displayed as a contour map or picture of the radiation pulse, is representative of the radiation intensity passing through the detector.

United States Patent [72] Inventors Thomas G. Roberts;

Charles M. Rust, both of Huntsville, Ala. 21 Appl. No. 881,028 [22]Filed Dec.1, 1969 [45] Patented June 15, 1971 [73] Assignee The UnitedStates of America, as

- represented by the Secretary of the Army [54] SIMPLE SOLID-ELECTROLYTEGAMMA-RAY AND RELATIVISTlC-CHARGED PARTICLE DOSIMETER 8 Claims, 4Drawing Figs.

[52] US. Cl 250/83, 250/833 [51] lnt.Cl G01t 1/04 [50] Field of Search250/83 CD, 83.3

[56] References Cited UNITED STATES PATENTS 2,708,242 5/1955 Ruben250/83 X 3,030,510 4/1962 Reeder 250/83 X 3,179,581 4/1965 Lewin et a1250/83 X Primary Examiner-Archie R. Borchelt Attorneys Harry M.Saragovitz, Edward J. Kelly, Herbert Berl and Harold W. Hilton ABSTRACT:A gamma-ray and relativistic charge particle detector and method formeasuring the amount of radiation passed through the detector. Thedetector is a dosimeter comprising a plurality of equally spacedbatteries disposed to form a series of columns and rows within a planehaving vertical and horizontal rectangular coordinate axes. Thebatteries, radiation sensors, can be repeatedly charged and dischargedwith very little characteristic change in the discharge curve. Thebatteries have a solid electrolyte and a low voltage output. Radiationpassing through the electrolyte causes partial ionization of theelectrolyte, which reduces the battery terminal voltage in proportion tothe amount and type of radiation passed therethrough. Before and afterbeing exposed to radiation, the batteries are placed in a test stand andthe individual battery voltages are simultaneously measured andrecorded. A change in voltage across the battery terminals, afterexposure to a known type of radiation, is proportional to the radiationpassed therethrough. Thus, differential voltage, displayed as a contourmap or picture of the radiation pulse, is representative of theradiation intensity passing through the detector.

24 /44 26 1 I l/ DISPLAY I e 29 H i/ i1 l-J l-J L-l L-l 2 I4 36 1O 3MULT- CHANNEL 2 l2 2 RECORDER L 36 I4 J P1 r1 1'! 1-1 32 20 f r -22 l l1 1 1 j SIMPLE SOLID-ELECTROLYTE GAMMA-RAY AND RELATIVISTIC-CHARGEDPARTICLE DOSIMETER BACKGROUND OF THE INVENTION Dosimetric instrumentsare designed for measurement of both random radiation and plannedradiation. These include the intermittent or continuous radiation of asample with a selected type of radiation, the random radiationencountered in handling radioactive material, and unexpected exposure tovarious radiation sources.

The radiation detector or dosimeter'converts ionizing radiation intorecordable energy such as electrical or chemical variations. A few ofthe detectors available in prior art devices include photographic films,chemical devices and calorimeters, which detect radiation such asX-rays, gamma and beta rays.

Quantitative measurements of high-intensity, short-duration pulses ofgamma-rays or electrons in the million-electron-volt (mev.) range arevery difficult, especially when the duration of these pulses are in thenanosecond range. Phototubes with proper shielding are currently beingused to measure the intensity of gamma-ray pulses but these are usuallyquite large because of the shielding required and each tube requires theuse of an expensive traveling wave oscilloscope. Thus little in the wayof spatial resolution may be obtained and the space behind the detectoris shielded from the radiation pulse, precluding use thereof.

Some chemicals which change luminosity properties or are stimulated toluminousness when radiated are also used with gamma-ray pulses. Somespatial resolution may be obtained with these chemicals, but each onemust be collected and expensive equipment must be utilized intime-consuming measurements.

For electron pulses, calorimeter arrays are used to measure beamprofiles and the total energy content of beams. Stacked thin sheets ofmetal are used as a calorimeter to measure the rate of loss of energyfrom which the energy of the electrons is calculated. Certain coloredplastics which have the property of changing when radiated are sometimesused with electron beams. These plastics must be calibrated with thecalorimeters, and the plastic is not produced for this purpose and thereare large variations even within the same plastics.

SUMMARY OF THE INVENTION The apparatus of the present invention is adevice for detecting and measuring the amount of high-intensity,short-duration pulses of gamma-rays or other ionizing radiation. Adetector includes a series of rechargeable, solid-electrolyte batteriesthat are thin enough to allow pulses of gamma-rays or electrons to bemonitored without appreciable attenuation thereof. The batteries arearranged in a plane for insertion between the radiation source and thesample to be radiated and are small enough to allow good spatialresolution to be obtained. They are fairly chemically inert and can bemounted in any position. Radiation impinging on the detector causes somesolid-electrolyte ionization in each battery that is proportional to theintensity of radiation. The ionization results in partial discharge ofthe batteries, thus decreasing the terminal voltage of each battery. Thedecreased terminal voltage is recorded and compared with the voltageprior to radiation sampling to display the radiation intensity as afunction of the change in voltage across the batteries. For a known typeof radiation, the change in voltage is indicative of the amount ofradiation passed therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a plan view of a preferredembodiment of the invention. FIG. 2 is a view along the line 2-2 of theembodiment of FIG. 1. FIG. 3 is a view along the line 3-3 of theembodiment of FIG. 1. FIG. 4 is a view of a detector and sample beingradiated.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawingswherein like numerals represent like parts in all figures, there isdisclosed a preferred embodiment of the invention in FIGS. 1, 2 and 3. Adosimeter 10 is mounted in a test jig 20 for electrical connection to amultichannel recorder 30. Dosimeter 10 includes a support structure 12for holding a plurality of batteries 14 therein. Batteries 14 aredisposed in a group of adjacent columns which form a series of evenlyspaced columns and rows within a plane. Test jig 20 includes a verticalsupport structure 22 attached to a bed 24 and to a pair of arms 26extending over bed 24. A slidable member 28 of jig 20 can be moved alongarms 26 and fixed in a desired position by screws 29. Support plates 32and 34 are respectively carried by plate 22 and member 28. A pluralityof electrical contacts 36 are carried by plates 32 and 34 and arealigned in parallel planes that are parallel with batteries 14 andsupport structure 12 so that an electrical contact 36 is on either sideand approximately coaxial with each battery 14. Electrical leads 40 fromeach contact 36 are brought together into a cable 42 for connection tomultichannel recorder 30. The recorded voltage levels can then becoupled to a graphical or visual display 44 for indicating the terminalvoltage of each battery. Visual display 44 may be a component part ofrecorder 30 or a remote display.

In FIG. 4, dosimeter 10 is placed between a sample or object 52 that isto be radiated and a radiation source 50. Source 50 is activated tostimulate emission of a known type of radiation which passes throughdosimeter 10 to reach the sample.

Batteries 14 can be individually charged to a selected low voltage orfor a prescribed period of time. Also, by removing recorder 30 andconnecting a charging source to cable 42, a plurality of batteries canbe simultaneously charged. Battery support structure 12 can be a thinplastic sheet and the batteries can be similar in shape and size to asmall coin, although these components are not limited to the structureas described.

In operation, a plurality of batteries 14 are charged to a low voltageby conventional means. The charged batteries in dosimeter 10 areinserted in test jig 20. Member 28 and plate 34 are pushed toward plate32 bringing the contacts 36 of plates 32 and 34 against the opposingsurfaces of each battery 14. Jig 20 is secured and recorder 30 isactivated to measure and record the open circuit voltage of each battery14. The recorder is then deactivated and dosimeter 10 is removed fromjig 20. Dosimeter 10 is placed in front of sample 52 and the radiationsource is pulsed. Radiation passing through dosimeter 10 causes someionization of the solid electrolyte therein in proportion to the amountof radiation passed therethrough. The batteries are partially dischargedbecause of the ionization which causes a decrease in the battery outputvoltage level. Dosimeter 10 is replaced in test jig 20 and the batteryterminal voltages are again measured and recorded by recorder 30. Thedifference in the two voltages measured across each battery is thendisplayed in any convenient form to give the intensity of radiation as afunction of battery position.

Regardless of the charge across each battery 14, passing of a known typeof radiation therethrough causes the charge to be reduced in proportionto the radiation. Therefore, the batteries can be used repeatedly untila minimum level of acceptability is reached, without recharging aftereach exposure and measurement.

Assuming ideal conditions, a plurality of batteries charged to the samelow voltage X will have the voltage X" recorded before exposure toradiation. If the sensors or batteries are arranged in a plane havingrectangular coordinate axes and the radiation source is aligned with anddirected toward the "0 or center of the axes as shown in FIG. 4, thecentermost sensor (battery) receives the greatest radiation withgradually lesser amounts received therearound. The sensors are thenrechecked to record the voltage changes.

thereacross. Graphically, a three-dimensional cone is produced,terminating at one end in the relatively flat surface bounded by thevoltage level X and terminating at the other end in a peak aligned withand approaching 0." Variations from this ideal situation obviously existwherein the battery voltages are not identical initially for allbatteries and radiation is directed toward the detector from variouslocations, for example. However, the differential voltage measuredacross each battery terminal is the critical information that indicatesthe amount of radiation passed through the battery. Each batterycontributes a voltage differential which determines the radiationcontour map or density of radiation measured.

Obviously, the sensors can be arranged other than in a rectangularcoordinate system. For example, a series of radii lying in a plane abouta given center point can have sensors at various locations on eachcircle around the point.

The batteries employed in dosimeter are similar to those described in anarticle in IEEE Transactions on Aerospace and Electronic Systems, VolumeAES-l, Number 3, Dec. 1965, pages 290-296. The article is entitledThin-Film Rechargeable Solid-Electrolyte Batteries."

Batteries 14 have long and stable shelf life, therefore the outputvoltage of each battery is constant in time and each battery isinsensitive to temperature changes. Because of the solid electrolytethey can be mounted in any convenient position. A typical battery can be0.025 centimeters thick and 1% centimeters in diameter or less in size.The batteries do not have to be mounted in a plastic holder, but can beglued or otherwise attached to the sample. The batteries can be mountedin badges or small holders worn by individuals and thereby provide meansof measuring the radiation dose that an individual has received while ina radiation area, or they can be placed so that they monitor theradiation in a given location.

When the batteries are placed in a given location they can beperiodically checked as previously described or they can be electricallyconnected to trip an alarm or activate a controlling circuit when thevoltage level drops below a preselected level due to radiation in thearea. In this capacity a typical electrical circuit can include aresistance bridge network with the batteries connected in series orparallel in a null circuit across the bridge. As radiation changes thebattery terminal voltage, the null is lost. A potentiometer or othersensor in the null branch responds to the change in potentialthereacross or current therethrough to activate heavy-duty electricalequipment, such as a relay, which in turn may sound an alarm, shut offoperating machinery, or initiate other desirable control steps. Placingthe batteries in a null condition eliminates any current drain therefromand in essence places them in a shelf storage state until radiationchanges the potential thereacross and breaks the null.

Similarly, a radiation-sensing battery can be connected in series with acurrent-sensing meter to activate an alarm circuit. A typical circuitcan include a direct current power source having a large resistancepotentiometer connected thereacross. One side of the potentiometer canbe connected to the meter and the variable arm connected to the batterysensor. The large resistance of the potentiometer allows only littlecurrent to drain from the source. The battery sensor is connected inopposition to the IR drop across the variable arm of the potentiometer.The potentiometer is adjusted to read a null on the meter, indicatingzero current flow. Radiation changes within the sensor cause animbalance to occur and current flow through the meter. At a preselectedlevel of current, the meter activates following circuitry.

We claim:

1. A gamma-ray and relativistic charge particle dosimeter comprising aplurality of radiation sensors arranged in a plane, each of said sensorshaving a known electrical potential thereacross and disposed to exhibita change in said potential in response to passage of radiationtherethrough.

2. Adosimeter as set forth in claim 1 wherein said radiation sensors aredirect current batteries.

3. A dosimeter as set forth in claim 2 wherein said batteries arerechargeable, solid-electrolyte and low-voltage-producing batterieswherein the solid electrolyte is partially ionized by radiation passingtherethrough to reduce the battery terminal or output voltage inproportion to the radiation passed therethrough.

4. A dosimeter as set forth in claim 3 wherein said batteries aredisposed to form a plurality of columns and rows in a plane havingvertical and horizontal rectangular coordinate axes.

5. A dosimeter as set forth in claim 4 wherein said plurality ofbatteries include at least four batteries, and each of said batterieshave a volume less than one-tenth of a cubic centimeter.

6. A method for measuring high-intensity, short-duration pulses of gammaradiation and relativistic charged particles comprising the steps of:

a. measuring the open circuit voltage level across each one of aplurality of radiation sensors,

b. subjecting the radiation sensors to an unknown amount of radiationfrom a known type of radiating source,

c. measuring the open circuit voltage level across each radiationsensor, and

d. comparing any change in the remeasured voltage from that of themeasured voltage of each sensor and thereby determining the amount ofradiation passed through each of said sensors as a proportion of thechange in voltage thereacross.

7. The measuring method as set forth in claim 6 and further comprisingthe steps of:

a. simultaneously measuring and remeasuring said sensors voltage levelby electrically connecting each of said sensors simultaneously to amultichannel recorder.

b. placing said plurality of radiation sensors in a plane between saidradiation source and a sample to be radiated and adjacent said sampleprior to subjecting radiation thereto for determining the radiationreceived by said sample, and

c. displaying said compared voltage differences from each sensor in adisplay showing the relative position of each sensor with respect toadjacent sensors and the amount of open-circuit voltage change for eachirradiated sensor,.

8. The measuring method as set forth in claim 7 and further comprisingthe steps of:

a. disposing said sensors to form a plurality of columns and rows in aplane having vertical and horizontal rectangular coordinate axes,

b. forming each of said radiation sensors from rechargeable, solidelectrolyte, direct current batteries having a volume less thanone-tenth of a cubic centimeter, and

c. subjecting said solid electrolyte to said unknown amount of radiationand thereby partially ionizing said electrolyte to reduce batteryterminal voltage in proportion to the amount of radiation passedtherethrough.

2. A dosimeter as set forth in claim 1 wherein said radiation sensorsare direct current batteries.
 3. A dosimeter as set forth in claim 2wherein said batteries are rechargeable, solid-electrolyte andlow-voltage-producing batteries wherein the solid electrolyte ispartially ionized by radiation passing therethrough to reduce thebattery terminal or output voltage in proportion to the radiation passedtherethrough.
 4. A dosimeter as set forth in claim 3 wherein saidbatteries are disposed to form a plurality of columns and rows in aplane having vertical and horizontal rectangular coordinate axes.
 5. Adosimeter as set forth in claim 4 wherein said plurality of batteriesinclude at least four batteries, and each of said batteries have avolume less than one-tenth of a cubic centimeter.
 6. A method formeasuring high-intensity, short-duration pulses of gamma radiation andrelativistic charged particles comprising the steps of: a. measuring theopen circuit voltage level across each one of a plurality of radiationsensors, b. subjecting the radiation sensors to an unknown amount ofradiation from a known type of radiating source, c. measuring the opencircuit voltage level across each radiation sensor, and d. comparing anychange in the remeasured voltage from that of the measured voltage ofeach sensor and thereby determining the amount of radiation passedthrough each of said sensors as a proportion of the change in voltagethereacross.
 7. The measuring method as set forth in claim 6 and furthercomprising the steps of: a. simultaneously measuring and remeasuringsaid sensors voltage level by electrically connecting each of saidsensors simultaneously to a multichannel recorder. b. placing saidplurality of radiation sensors in a plane between said radiation sourceand a sample to be radiated and adjacent said sample prior to subjectingradiation thereto for determining the radiation received by said sample,and c. displaying said compared voltage differences from eacH sensor ina display showing the relative position of each sensor with respect toadjacent sensors and the amount of open-circuit voltage change for eachirradiated sensor,.
 8. The measuring method as set forth in claim 7 andfurther comprising the steps of: a. disposing said sensors to form aplurality of columns and rows in a plane having vertical and horizontalrectangular coordinate axes, b. forming each of said radiation sensorsfrom rechargeable, solid electrolyte, direct current batteries having avolume less than one-tenth of a cubic centimeter, and c. subjecting saidsolid electrolyte to said unknown amount of radiation and therebypartially ionizing said electrolyte to reduce battery terminal voltagein proportion to the amount of radiation passed therethrough.